1. Field of the Invention
The invention relates to a web anti-wrap device for a web printing press for preventing a broken web from wrapping around the printing cylinders of the printing press.
2. Description of Related Art
There has been generally used a web printing press which comprises a plurality of printing units arranged in a web feeding direction. The printing units each includes printing cylinders such as blanket cylinders and plate cylinders, through which a web is fed to be printed. The printing press further comprises a dryer unit, a chill unit and a folder unit which are disposed downstream of the printing cylinders in the last printing unit. The printed web is discharged from the last printing unit and directed into and heated in the dryer unit. The web is then directed into and cooled in the chill unit and directed into and folded in the folder unit.
In the printing press, the web may be accidentally broken by thermal stresses in the dryer unit or the chill unit. The web may also be accidentally broken by fluctuating tensions in the folder unit. The printing press is slowed and stopped in response to a signal from a detector detecting the web break. However, before the printing press is stopped, the broken web may be directed back to and wrapped around the printing cylinders. This results in substantial down time for removing the wrapped web from the printing cylinders. When the broken web is wrapped around a blanket cylinder including a blanket, the blanket may be damaged by the wrapped web. It is therefore required to frequently exchange the blankets for new ones, involving an expense.
In order to overcome the problems, there has been proposed a web anti-wrap device as disclosed in U.S. Pat. No. 5,398,610 and U.S. Pat. No. 5,443,008. The anti-wrap device includes anti-wrap means comprising upper and lower anti-wrap rollers which are disposed between the last printing unit and the dryer unit. The anti-wrap rollers are engaged with each other when the web is broken, to capture the broken web therebetween and pull it from the last printing unit for preventing the broken web from wrapping around the printing cylinders. The web is directed from the last printing unit by the anti-wrap rollers and harmlessly gathered in a shop floor space between the anti-wrap rollers and the dryer unit.
Under the circumstances, in the existing presses as well, an attempt has been made to additionally install the anti-wrap means between the last printing unit and the dryer unit. However, it has a problem with respect to the space between the last printing unit and the dryer unit. A limited space as the existing press has between the last printing unit and the dryer unit, the space is intended to utilize for making preparations for the printing operation. For example, an operator use the space to mount plates onto the plate cylinders. The operator then inspects in the space how the plates are mounted on the plate cylinders. It is also required to inspect in the space the dirt of the plates. The operator further use the space to exchange the blankets of the blanket cylinders for new ones. It is also required to watch in the space the ink and dampening water in the printing press.
On the other hand, in order to additionally install the anti-wrap means between the last printing unit and the dryer unit in the existing press, it is required to position the anti-wrap means apart from the dryer unit so as to create a shop floor space therebetween so that the broken web can be harmlessly gathered in the shop floor space when directed from the the last printing unit by the anti-wrap means. In addition, the anti-wrap means should include detectors for detecting a web break, as described in the above U.S. Patents. It is therefore required to position the anti-wrap means apart from the dryer unit so as to keep the anti-wrap means from being heated by the dryer unit, otherwise the detectors may be damaged. In this connection, it is not permissible to position the anti-wrap means apart from the last printing unit so as to create a working space between the anti-wrap means and the last printing unit for making preparations for the printing operation. The operator is hindered from making preparations by the anti-wrap means.
On the contrary, it may be also desired to create a working space between the anti-wrap means and the dryer unit for maintenance of the dryer unit.
It is therefore an object of the invention to provide a new and improved web anti-wrap device for a web printing press, to thereby overcome the above problems.
Another object of the invention is to additionally install anti-wrap means between printing cylinders and a processing device which is disposed downstream of the printing cylinders in the existing press, to prevent a broken web from wrapping around the printing cylinders.
Other object of the invention is to create a shop floor space between the anti-wrap means and the processing device so that the broken web can be harmlessly gathered in the shop floor space.
Other object of the invention is to keep the anti-wrap means from being heated by the processing device which comprises a dryer unit.
Other object of the invention is to create a working space between the anti-wrap means and the printing cylinders or between the anti-wrap means and the processing device.